This work deals with investigations of fluorescence phenomena during interaction of ultraviolet laser radiation with four substances (2,5-dihydroxybenzoic acid, 3-hydroxypicolinic acid, dithranol and ferulic acid) commonly used as matrices in matrix-assisted laser desorption/ionization (MALDI). Wavelength-resolved fluorescence measurements allowed classification of UV- MALDI matrices on the basis of their Stokes shift. Matrices showing a high Stokes shift dissipated high amounts of laser energy by means of intra- and intermolecular energy transfer processes, hence contributing less to the ionization of analyte compounds. Conversely, matrix substances with a low Stokes shift retained more of the original photonic energy which may then be available for ionization within the matrix or after desorption of molecular species. Therefore matrix compounds can be designated as "hard" (high ionization energy) in the case of small Stokes shifts or "soft" (low ionization energy) in the case of high Stokes shifts. Time-resolved measurements showed fluorescence lifetimes below 5 ns for all four substances.

Keywords: fluorescence matrix substance, fluorescence lifetime matrix, matrix-assisted laser desorption/ionization (MALDI) fluorescence, matrix energy conversion, matrix Stokes shift, spectroscopy matrix-assisted laser desorption/ionization (MALDI) desorption process